2 TYPES OF NODULES INDUCED ON TRIFOLIUM-PRATENSE BY MUTANTS OF RHIZOBIUM-LEGUMINOSARUM BV TRIFOLII DEFICIENT IN EXOPOLYSACCHARIDE PRODUCTION

Several Tn5 mutants of the symbiotic bacterium Rhizobium leguminosarum by. trifolii 24.1 that fail to synthesize acidic exopolysaccharide, a re able to induce non-nitrogen-fixing nodules on Trifolium pratense. H ybridization analysis indicated that Tn5 insertions were located on me gaplasmids pRtb and pRtc and on the chromosome of R. leguminosarum by. trifolii 24.1. Microscopic analysis of nodules induced by these non-m ucoid mutants revealed two types of nodules: infected nodules with inf ection threads and bacteroids, and non-infected nodules which neither contained infection threads nor bacteroids. Ultrastructural data on ba cteroid development and plant cell differentiation in nodules induced by the mutants indicate a decrease in bacteroid and plant metabolism. Starch accumulation in the plant plastids and presence of osmiophilic droplets in the plant cells of the peripheral tissue was observed.